The present nonprovisional application claims priority under 35 USC 119 to Japanese Patent Application No. 2001-400627 filed on Dec. 28, 2001 the entire contents thereof is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a liquid pressure type steering damper system for vehicles which is preferable for saddle ride type vehicles such as motorcycles and the like and is used for restraining the swing of a handle during operation.
2. Description of Background Art
In order to prevent the handle from being swung due to a kick-back upon a disturbance, liquid pressure type steering damper systems which generate a damping force against the swing have been known, for example, as disclosed in Japanese Patent No. 2593461. In addition, systems in which the damping force is variable so that the damping force is generated only when required and a needless damping force is not generated in other situations have also been known; for example, a system which controls the damping force based on steering angle and operating velocity as disclosed in Japanese Patent Laid-open No. Sho 63-64888. In addition, a system which controls the damping force based on variations in the load on the front wheel is disclosed in Japanese Patent Publication No. Hei 7-74023.
In the damping force variable type steering dampers according to the above-mentioned related art examples, a sensor quantity detected and a damping force quantity generated, which are used for controlling the damping force, are considered to be in a linear relationship. However, with such a linear relationship, the front wheel steering system would steer more largely before the generation of a required damping force as the kick-back to be generated due to a disturbance is greater. Therefore, it is desired to prevent a large kick-back by generating a damping force swiftly and appropriately, without causing a large extent of steering.
In addition, if the generation of a needlessly great damping force is allowed, the steering damper is required to have a needlessly high strength for enduring the excessively large damping force. Therefore, it is also desired that an excessively large damping force is not generated. Accordingly, it is an object of the present invention to realize the above-mentioned requests.
In order to solve the above-mentioned problems, the present invention provides a steering damper system wherein a steering damper system of the liquid pressure type in which a damping force is exerted on a front wheel steering system provided at a front portion of a vehicle body and which includes a control valve for making the damping force variable with the control valve including a valve body advancing and retracting in a passage for the working liquid and wherein the valve body has a thickness varying uniformly along the longitudinal direction thereof. The advancing/retracting motions of the valve body make the clearance area of a gap passage formed around the valve body variable with the clearance area being varied nonlinearly in relation to the advancing/retracting stroke of the valve body. The damping force generated at the gap passage is increased in a manner of a quadric curve in relation to variations in the stroke.
The present invention includes the cross-sectional shape of the gap passage that is in an annular shape.
The present invention provides a control valve that includes an upper limit restricting means for restricting the generation of the damping force to be not more than a predetermined upper limit.
The present invention includes a control valve that is a solenoid valve, and the upper limit restriction of the damping force is effected by an electromagnetic force of the solenoid valve.
According to the present invention, the variation of the clearance area of the gap passage formed around the valve body is varied nonlinearly in relation to the stroke amount of the valve body which advances and retracts, whereby the damping force generated at the gap passage is increased in the manner of a quadric curve in relation to the variations in the stroke. Therefore, since the damping force is increased rapidly as the kick-back generated is greater, a great kick-back can be effectively prevented by generating the damping force swiftly and appropriately, without causing the front wheel steering system to steer to a large extent.
According to the present invention, the gap passage is annular, so that the clearance area varies in the manner of a square in relation to the variation in the radius of the gap passage which is proportional to the stroke amount of the valve body attendant on the advancing/retracting motions of the valve body. Therefore, the variation of the clearance area in the manner of a quadric curve mentioned above can be realized easily and with a comparatively simple structure because it suffices that the restriction passage and the valve body are formed to be circular in cross section.
According to the present invention, the control valve comprises the upper limit restricting means, so that the generation of the damping force can be restricted to a required level even when the damping force increases rapidly in the manner of a quadric curve. Therefore, it is unnecessary to provide the steering damper with a needlessly high strength.
According to the present invention, the control valve is a solenoid valve, whereby it is ensured that even if a damping force greater than the electromagnetic force of the solenoid valve tends to be generated, the generation of an excessively large damping force is hampered because the solenoid valve is opened by the liquid pressure. Therefore, the upper limit restricting means can be composed with a simple structure in which the control valve is simply a solenoid valve. Accordingly, it is unnecessary to separately provide a special upper limit restricting means.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.